Commercial freezing systems have included a housing defining a tunnel through which runs an endless conveyor which is constructed from mesh or the like. The food preparations to be frozen are placed on the conveyor and transported through the tunnel. A number of fans are disposed along the length of the tunnel in order to circulate a cooling atmosphere.
The cooling atmosphere is desirably circulated past the food and through the conveyor and back around to the fans in order to achieve an efficient freezing operation. However, a large quantity of the cooling atmosphere is circulated above the conveyor and therefore not used effectively to freeze the food moving through the tunnel.
In order to overcome this problem it has been proposed to establish a secondary flow of cooling atmosphere below and parallel to the length of the conveyor, thereby creating a venturi effect and causing the cooling atmosphere to move past the food and through the conveyor. This secondary flow of the cooling atmosphere requires the use of additional internal motors to produce the necessary circulation of the atmosphere. However, the heat generated by these additional motors reduces the overall efficiency of the freezing operation within the tunnel.
As the number of the motors is increased and the power of each motor is raised to maximize the venturi effect, there is a corresponding increase in the amount of heat generated which reduces cooling efficiency. Such tunnels are also disadvantageous because they do not effectively prevent the escape of the cooling atmosphere from the tunnel exit.
The spraying zone of conventional freezing systems also inadequately preserve the cooling atmosphere. It is desirable that the atmosphere in the spraying zone, which is the coldest in the tunnel, be evenly distributed across the width of the conveyor to insure uniform cooling of the product. The use of curtains at either end of the spraying zone has been contemplated, however, these fail to provide sufficient isolation from the circulating atmosphere in adjacent zones.
It would, therefore, be desirable to provide a freezing system which efficiently circulates the cooling atmosphere past the food and through the conveyor without the use of expensive secondary cooling devices.